This invention relates in general to improved seals for drill bit bearings and in particular to seals which resist deformation and distortion in response to increased loading.
Earth-boring drill bits, such as are typically employed in the petrochemical industry for drilling oil or gas wells, are rugged pieces of equipment which must operate in very severe environments. In such operations, a drill bit is typically threaded on to a section of pipe and lowered into a well bore wherein it is rotated for the purpose of cutting through rock and earth formations. Rotatable cutters are usually mounted on a shaftlike cutter support and the fragments of rock created by the operation of the rolling cutters are removed from the well bore utilizing a drilling fluid or "mud" solution. In prior art drill bits, several solutions have been proposed to inhibit the ingress of abrasive detritus into the bearings of the rolling cutter thereby permitting the rolling cutter to be operated over extended periods of time in this environment. One such solution to this problem has been the utilization of pressure equalized lubricant reservoirs which are operated by the pressures of the drilling fluid within the well bore and which serve to equalize the pressure of the lubricant with the exterior pressures around the bit to maintain lubricant on the bearing surfaces. This pressurized lubricant reservoir has been moderately successful in preventing the ingress of abrasive detritus into the bearing area; however, the pressure equalized lubricant reservoir does result in the egress of lubricants from the bearing area in greater amounts than is normally desired.
Another approach to the problem of preventing abrasive material from wearing away at the bearing surfaces has been the utilization of various ring sealing devices. An early example of this approach may be seen in U.S. Pat. No. 3,397,928, issued to Edward M. Galle. The Galle disclosure teaches the simple expedient of an elastomeric sealing ring which has been compressed between the inner face of the rolling cutter and the cutter shaft. Another example of a packing ring seal utilized in rotary drill bits may be seen in U.S. Pat. No. 3,656,764, issued to William P. Robinson. The Robinson drill bit seal assembly utilizes two elastomeric O-ring seals which are separated by a rigid ring which is utilized to seat the O-rings into opposing bearing surfaces. This utilization of a rigid ring allegedly provides an increase in accommodation of radial, axial and angular displacements over previously known O-ring seals. A third example of sealing ring devices can been seen in U.S. Pat. No. 3,137,508, issued to R. A. Cunningham. The Cunningham seal comprises a frusto-conical metallic ring which is lightly encapsulated with a resilient lubricant resistant material at those areas which form seals for rotating metal surfaces.
Each of these sealing mechanisms and pressure equalized lubrication systems is designed to prevent the ingress of abrasive detritus into the bearing support in the rolling cutters. This is necessary since it is most desirable to operate the drill bit for long periods of time between drill bit changes, due to the amount of manpower and time required to remove the drill stem from the well bore to replace the drill bit. Complicating this problem is the fact that fluctuations in position and pressure which are encountered by an earth-boring drill bit during operation are substantial and tend to displace the rolling cutter from the shaft upon which it is mounted. One method of sealing the bearing supporting drill bit rolling cutters which accommodate such displacements is the so-called "face" seal which is disposed between a surface of the rolling cutter and a face surface of the drill bit body. Such seals generally provide a similar compression whether loaded or unloaded and provide an excellent seal.
A second form of seal is the so-called "shaft" seal or radial seal which is disposed about each shaft on a drill bit body and which is then compressed radially. These seals provide an excellent method of preventing the ingress of abrasive detritus; however, the loading experienced by a rolling cone cutter often has a tendency to "load" or increase the compression on one side of the shaft and "unload" or decrease the seal compression on the other side of the shaft. Accordingly, there exists a need for a shaft seal which does not substantially change in compression and response to radial loading of the rolling cone cutters.